1. Field of the Invention
This invention relates to asphalt surfacing compositions which are particularly useful in paving construction. The compositions of this invention exhibit improved elasticity and improved adhesion of the asphalt binder to the mineral aggregate. Both the propoxylated asphalt and the silane, if employed, contribute to the improved adhesion properties of these compositions.
2. Description of the Prior Art
A wide variety of compounds have been added to asphalt surfacing compositions in an attempt to improve the adhesion of the asphalt to the mineral aggregate and in attempts to improve the elasticity in such compositions.
A wide variety of silicon compounds including silanes have been used for the impregnation and surface treatment of glass fibers to promote the adhesion of various organic resins such as the polyester resins, epoxide resins or phenol formaldehyde resins and for the surface treatment of textiles, leathers, ceramics and glass materials.
It has been found that the adhesion of asphalt to siliceous aggregates could be markedly improved by first treating the aggregate with vapors of a mixture of methylchlorosilanes. This method, which is rather exotic, is not practical in large scale applications. Sanderson, F. C., "Methylchlorosilanes as Anti-stripping Agents". Proceedings, Highway Research Board, 31,288 (1952).
A great number of patents, particularly those in class 106, subclasses 273 and 277 disclose many compositions and processes for improving the adhesion of asphalt binders to mineral aggregate. The patent literature referring to silicon compound chemistry continually is concerned with the thermal stability of silicon compounds. The most desirable compounds for use as adhesion promoters must promote the adhesion of asphalt to mineral aggregate and remain stable over a wide temperature range and for an extended period. In addition to this it is highly desirable that the adhesion promoters be capable of being used without exotic application methods. Preferably it should be possible to introduce the promoter into the asphalt in the molten state or to apply it to the mineral aggregate prior to mixing with the asphalt or both.